A method for formation of an organic layer in organic electroluminescent elements includes a vacuum evaporation method and a wet film formation method. A vacuum evaporation method enables easy lamination and therefore has the advantage of improving charge injection from anode and/or cathode and facilitating exciton blocking in light-emitting layer. On the other hand, a wet film formation method does not require a vacuum process and therefore has the advantage that it enables large-area film formation and makes it possible to mix multiple materials having different functions in forming one layer and preparing a coating liquid for the layer. However, according to the wet film formation method, lamination is difficult. Consequently, as compared with elements produced according to a vacuum evaporation method, those produced according to the wet film formation method are poor in driving stability, and except for a few, they could not be on a practicable level as yet. In particular, lamination of two layers would be possible according to the wet film formation method using an organic solvent and an aqueous solvent, but lamination of three or more layers is still difficult.
For solving the problems with lamination, PTL 1 proposes a polymer (Q-1) having a fluorene ring and a crosslinking group as described below, and discloses lamination of multiple layers by utilizing the phenomenon that the network polymer to be formed through reaction of the crosslinking group by heating becomes insoluble in an organic solvent.

PTL 2 reports film formation by the use of a polymer having both a branched structure and a crosslinking moiety, under milder heating conditions.